Author(s):
ZULKIFLI Hashim* ; AHMAD TARMIZI Hashim*

In an incubation experiment, P was added to the Rengam Series soil through empty fruit bunches (EFB) alone (38 mg P kg-1 soil), P fertilizer alone (900 mg P kg-1 soil), and P fertilizer added together with EFB (938 mg P kg-1 soil). The P fertilizers used were triple superphosphate (TSP), Gafsa (Tunisia) phosphate rock (GPR) and Christmas Island phosphate rock (CIPR). For each month during the six-month incubation, soil P fractions, namely iron oxide-coated strip P (Pi), Bray 2 P, NaOH P, occluded P, Ca P, organic P, microbial biomass P, total P, amount of P dissolved (DP) from phosphate rock (PR), and exchangeable Ca were determined. The percentage dissolution of TSP, GPR and CIPR was 94.8%, 31.3% and 26.6% of added P, respectively, following the chemical reactivity of the materials. Addition of organic residues (EFB) only had a significant effect on the dissolution of CIPR. However, the results show a positive influence of organic residues added with P fertilizer which stimulated the formation of microbial biomass P (four times more than with P fertilizer added alone), organic P (about two times more than with P fertilizer added alone), and less movement into the inorganic P fractions. Addition of organic residues led to the continued increase in dissolution of PR with time, over the six months of incubation, compared to when PR alone was added to the soil; this might be due to the additional sinks for P (biological transformation of P) and Ca (increase in Ca-exchange sites).